In the second part of the Animated Fish Swarm In Blender tutorial, Frederik Steinmetz shows you how to take advantage of instance rendering in Cycles. He will reveal an effective way to composite a Blender rendering on top of a Cycles rendering, without having to make a copy of the entire scene, or temporarily store your render results in EXR files. However you'll still be able to take advantage of Blender's motion blur as well as halo spotlight effects.